The present invention relates generally to the field of microwave imaging, and more specifically to an improved antenna design for microwave imaging of the human body.
Microwave imaging systems have found use in detection applications including determining the presence and location of unseen objects based on the reflections of microwave radiation. Microwave imaging systems illuminate a target, such as a part of the human body, having specific dielectric properties, with electromagnetic (EM) waves, which penetrate the target and interact with the interior. The waves are then reflected back from objects within the target and their properties are monitored to determine presence and location information. Most dielectric materials such as clothing, paper, and plastic are nearly transparent over the spectral band of microwave radiation, thus microwave imaging have proven to be beneficial in a variety of applications including security inspection systems. Perhaps most appealing is the fact that microwaves are nonionizing at moderate power levels. Thus microwave radiation has the distinct advantage over other sources of radiation of not posing a health risk to human patients. As a result, microwaves appear well suited to biological sensing applications including early detection of breast cancer. Microwave imaging overcomes several limitations of other early-stage breast cancer detection systems such as Magnetic Resonance Imaging (MRI) and X-ray mammography that expose patients to low levels of ionizing radiation. Mammography is also uncomfortable for patients as breast compression is required to reduce image blurring and to create tissue uniformity. At microwave frequencies, however, a significant dielectric contrast between normal and malignant tissue is found. Typical breast tissue, for instance, has a relative dielectric constant of about 10, while a malignant tumor has a relative dielectric constant in the range of 45-55. This results in less attenuation and reflection from the normal tissue than from malignant tissues. Malignant tumors will create microwave scattering cross-sections much larger than that of normal breast tissue of the same size. Further, healthy, fatty tissues are relatively translucent to microwaves since attenuation in normal breast tissue is low enough to make signal propagation through even large breast volumes quite feasible. Microwave imaging is therefore a safe, comfortable, and accurate method for the early detection of breast cancer.